To achieve a high-quality health care system, medical providers need ready access to actionable health information. Fragmentation of care in our current system results in missing information, leading to inefficiencies and suboptimal medical decision making. By providing a free flow of information, electronic health information exchange (HIE) is a promising method for improving the efficiency and quality of care. If efficiency gains from HIE (such as a reduction in duplicative and unnecessary testing) can be established, it may motivate medical payers to subsidize HIE efforts that improve the health care system more broadly. Current evidence that HIE reduces test utilization is, however, scant and inconclusive. Mesa County, Colorado provides a rich resource for more definitive assessment of the effects of HIE. Quality Health Network started providing HIE to Mesa County in 2005, captures nearly all the test results in the County, and has been adopted by over 351 practitioners (over 85% of County practitioners). There is also evidence that reductions in laboratory and radiology utilization since the introduction HIE in Mesa County contrast with national trends of steady or increasing test utilization. This study will formally assess whether adoption of HIE is associated with a reduction in utilization of laboratory and radiology testing in Mesa County. It will also assess whether the effects of HIE are more pronounced in when care is more fragmented (circumstances in which patients receive care from more than one practice). Combining practice-level information from Quality Health Network and claims data from 2004 through 2009 from the primary commercial health plan in the area, a differences-in-differences model will be employed to distinguish the effects of HIE adoption from secular trends in test utilization. The results of this study will guide future HIE efforts, and will provide estimates of value that will prove useful for national decision makers and local stakeholders in HIE. Its goals are directly relevant to AHRQ's investments in HIE projects, and AHRQ's general mission to promote and assess the use of health information technology to improve healthcare quality and efficiency. PUBLIC HEALTH RELEVANCE: The electronic exchange of health information in communities may improve the quality and efficiency of medical care. Doctors can make better decisions when the health information they need is at hand. By assessing whether a robust, mature regional health information exchange system helped doctors provide more efficient medical care, this project will inform local and national stakeholders in health information exchange efforts.